1. Field of the Invention
The present invention relates to electrical and electronic circuits and systems. More specifically, the present invention relates to microwave Class E power amplifiers.
2. Description of the Related Art
For a variety of commercial and military applications, highly efficient microwave and radio frequency (RF) power amplifiers are needed. Typical applications include wireless local area networks, cell phones and telecommunication systems as well as advanced airborne active phased array radar systems. The choice of technology, design methodology and manufacturing cycle time are major cost contributors in these systems. Switching mode, Class-E, high-efficiency power amplifiers are useful for these and other applications inasmuch as these amplifiers limit the power and associated cooling costs thereof. A Class-E amplifier is part of the “switching mode amplifiers” such as class D, E, F, etc. In these types of amplifiers, the transistor operates as a perfect switch with no overlapping voltage & current waveforms at its output terminal, thereby ideally dissipating zero DC power. Other classes of amplifiers such as class A, A/B and C, operate as a current-source with overlapping voltage & current waveforms and hence dissipate DC power leading to a lower efficiency.
Class-E amplifiers use a series or parallel resonant load network. The function of the load network in the class E amplifier is to shape the voltage and current waveforms. The current and voltage time-waveforms at the active device output terminal are optimized in such a way as to minimize the DC power dissipation within. The active device, a pHEMT in this case, acts as a switch, driven by the RF input signal to “ON” and “OFF” conditions. The operating point of the device is such that the device is either OFF (in the pinched-off region) or ON (in the linear region). Under an ideal switching operation condition, output voltage and current waveforms at the device output terminal do not exist simultaneously and, therefore, the energy dissipated within the device is zero, yielding a 100 percent theoretical power conversion efficiency.
In any event, the maximum efficiency of Class-E amplifiers (i.e. the ratio of the RF output power to the DC input power) and its bandwidth of operation are limited by the tuned loads thereof. The limitation is due to the fact that presence of the tuned load results in a very narrow operational bandwidth for the amplifier.
Hence, a need remains in the art for a system or method for increasing the power, power added efficiency (PAE) and bandwidth of Class-E amplifiers.